ABSTRACT The goal of the Targeted DNA Methylation & Mitochondrial Heteroplasmy Core is to provide researchers studying aging and age-related diseases with state-of-the-art molecular analyses that are not available at institutional cores. The Core focuses on DNA methylation and mitochondrial heteroplasmy because we have developed novel technologies that address fundamental questions of how genomes change with age. DNA methylation is a major regulator of gene expression; studies show that DNA methylation patterns change with aging, and these changes can be caused by a wide variety of environmental stimuli at any point in the lifespan. As a fundamental regulator of gene expression, altered DNA methylation patterns could cause genes to be aberrantly expressed (e.g., cancer) or suppress genes required for continued cellular function (e.g., senescence). On the other hand, increases in mutations and deletions in the mitochondrial genome (mtDNA) with age have been known for some time, but the field has struggled because assays that lack coverage across the entire mitochondrial genome and have limited quantitative accuracy. Accurate and comprehensive analyses of mtDNA will provide data that define the contributions of mtDNA changes to mitochondrial dysfunction. This Core will enable Geroscience researchers to utilize DNA methylation and mitochondrial (mtDNA) heteroplasmy analyses in their research programs by providing unique assays, instrumentation not present in individual laboratories, and technical expertise to generate and analyze the data from these studies. The specific aims of the DNA Methylation & Mitochondrial Heteroplasmy Core are: Aim 1. Perform quantitatively-accurate DNA methylation analyses, ranging from genome- wide to gene-specific, using advanced sequencing technologies. Aim 2. Measure mitochondrial genome heteroplasmy and copy number with new methods that allow for comprehensive variant analysis and absolute genome copy number quantification Aim 3. Develop DNA methylation assays for exceptionally long-lived animals and mitochondrial heteroplasmy analyses for invertebrates (e.g., Drosophila, C. elegans, and yeast) and exceptionally long-lived animals.